NAND flash memory, as well as other types of non-volatile memories (“NVMs”), are commonly used in electronic devices for mass storage. For example, consumer electronics such as portable media players often include flash memory to store music, videos, and other media.
Non-volatile memories, however, may develop defective memory cells through everyday use, and operational memory cells may suffer from program/erase/read disturb due to voltages applied to neighboring cells. When a memory location, such as a page, of a NVM contains too many defective cells or otherwise becomes unusable from excessive errors, the information contained within that memory location may be lost. When this occurs, the electronic device using the NVM might lose user data (e.g., data stored by an application). In addition, the electronic device might lose metadata that the electronic device uses to manage the NVM. When the user data or metadata of particular memory location is affected to such an extent that it cannot be corrected using an error correction code, that memory location has experienced an uncorrectable error.
In some operations such as garbage collection, the occurrence of an uncorrectable error (e.g., an unreadable memory location) can have substantial adverse effect on the management of the NVM.